U.S. application Ser. No. 327,597, filed concurrently herewith by the present inventors, titled Method of Making An Electrode Assembly, points out that there are numerous types of electronic devices, such as dot matrix display panels, which involve the use of two sets of electrodes spaced apart but in operative relation with one another. The text also notes that the electrodes are supported and separated by a body of electrical insulating material in which are located slots, holes, grooves, or other open passages which are frequently difficult to make and, consequently, greatly increase the cost of the assemblies.
A discussion is also provided disclosing the prior use of glasses, glass-ceramics, and ceramics for fabricating supporting structures for use in electronic devices, and the problems encountered. Glasses, glass-ceramics, and sintered ceramics demonstrate high refractoriness, good chemical resistance to the ambient environment, relative inertness to impinging radiations of various wavelengths, and high mechanical strength but are difficult to drill, punch, or otherwise mechanically shape into complex geometries.
Finally, U.S. Pat. Nos. 2,628,160, dated Feb. 10, 1953, 2,684,911, dated July 27, 1954, and 2,971,853, dated Feb. 14, 1961, of Stanley D. Stookey, are reviewed. The first two patents describe thermally opacifiable glass compotions which exhibit photosensitivity and the capability of being chemically machined to fine tolerances, and the third patent describes the production of glass-ceramic bodies which also demonstrate photosensitivity and the capability of being chemically sculptured.
The opal glasses described consist essentially, expressed in weight percent on the oxide basis, of 9-15% Li.sub.2 O, 0-8% total Na.sub.2 O and/or K.sub.2 O, 9-23% Li.sub.2 O+Na.sub.2 O+K.sub.2 O, 70-85% SiO.sub.2, 0.001-0.020% Ag, computed as AgCl, 0-10% Al.sub.2 O.sub.3, 0-2.4% F, and 0-0.05% CeO.sub.2. When portions of such glass bodies are exposed to short wave radiation, customarily ultraviolet radiation, a latent image is produced in those portions. Subsequent heat treatment of at least those portions of the glass bodies at temperatures generally below the softening point of the glass causes the development of crystallites of a lithium silicate and/or an alkali metal fluoride therein which impart opacity thereto. Those crystals are much more soluble in mineral acids, e.g., dilute hydrofluoric acid, than the surrounding glass. Advantage has been taken of this solubility differential between the crystallites and the residual glass to implement the chemical machining or sculpturing of such glass articles into very complex configurations and to produce holes therein without the need for mechanical tools.
The glass-ceramic articles disclosed in U.S. Pat. No. 2,971,853 consist essentially, expressed in weight percent on the oxide basis, of 60-85% SiO.sub.2, 5.5-15% Li.sub.2 O, 2-25% Al.sub.2 O.sub.3, the ratio Al.sub.2 O.sub.3 :Li.sub.2 O being less than 1.7:1, and a photosensitive metal in the indicated proportions selected from the group of 0.001-0.03% gold, computed as Au, 0.001-0.3% silver, computed as AgCl, and 0.001-1% copper, computed as CuO. When portions of glass bodies having compositions within those cited ranges are exposed to short wave radiation, normally ultraviolet radiation, a latent image is produced in those portions. Thereafter, at least those previously-exposed areas of glass bodies are subjected to a two-step heat treatment. Thus, those portions are initially subjected to temperatures between the annealing and softening points of the glass, and then to temperatures above the softening point of the glass. This latter step effects crystallization in situ in the previously-exposed portions of the bodies, the unexposed portions being essentially unchanged. The exposed areas are highly crystalline and include at least one lithium-containing crystal phase which is more readily soluble in mineral acids, e.g., dilute hydrofluoric acid, than the residual glass. These glass-ceramic articles are mechanically stronger and possess the capability of being used in higher temperature applications than the above-discussed photosensitive opal glasses.
Chemically-sculpturable, photosensitive glasses and glass-ceramics have been employed commercially in a number of applications including electronic and fluidic devices where grooves, slots, holes, etc., of high tolerances have been etched therein. For example, Corning Glass Works, Corning, New York, has marketed a chemically machinable, photosensitive glass product under the trademark FOTOFORM and chemically machinable glass-ceramic product under the trademark FOTOCERAM.